1. Field of the Invention
The present invention relates to a hammer drill capable of giving rotation and/or impact to a bit at a top end thereof.
2. Description of the Background Art
As shown, for example, in patent document 1, a hammer drill having the following structure has been known: a hammer drill includes a tool holder supported at a front part in a housing, an impact mechanism provided at a rear part of the housing, an intermediate spindle supported in parallel with the tool holder at a lower part of the impact mechanism. The tool holder holds a bit at a front end thereof, and the impact mechanism has a reciprocating impact piece for indirectly impacting the bit via an intermediate piece. A rotation of an output spindle of a motor is transmitted to the intermediate spindle, at which a clutch member, a second gear (a rotation transmitting member), a boss sleeve (an impact transmitting member) and a switching lever (a mode switching member) are provided. The clutch member has clutch pawls on both faces thereof and is capable of integrally rotating with the intermediate spindle and sliding in a spindle direction. The second gear is loosely fitted to the intermediate spindle at a front part of the clutch member, has a pawl for engaging with the clutch, and meshes with a gear at the tool holder side. The boss sleeve is loosely fitted to the intermediate spindle at a rear part of the clutch member, has a pawl for engaging with the clutch, and converts the rotation of the intermediate spindle to a fore and aft movement so as to transmit the movement to the impact mechanism. The switching lever has a pushing piece (an engaging pin) provided at an eccentric position thereof, where the pressing piece fits to a tapered face provided around the periphery of the clutch member.
That is, the clutch member is slid by an eccentric movement of the pressing piece by a rotating operation of the switching lever, so that the clutch member is engaged with and released from the second gear and/or the boss sleeve. As a result, a user can select one of modes of which a drill mode for engaging the clutch member with only the second gear to give only rotation to the bit, a hammer drill mode for engaging the clutch member with both the second gear and the boss sleeve to give rotation and impact to the bit, or a hammer mode for engaging the clutch member with only the boss sleeve to give only impact to the bit. As a result, the mode can be switched smoothly with a simple structure, and thus wear and heat generation of the member due to switching of the mode can be suppressed, and excellent durability can be acquired.
Patent document 1: Japanese patent No. 3168363